docs: def _preprocess_data(self, data):
          """Converts the data array to the preferred dim x #points structure.
  
          Parameters
          ----------
          data : :obj:`numpy.ndarray` of float
              The data to process.
  
          Returns
          -------
          :obj:`numpy.ndarray` of float
              The same data array, but reshapes lists to be dim x 1.
          """
          if len(data.shape) == 1: 
              data = data[:,np.newaxis]
          return data